The hydration process using a nitrile compound as a raw material is used as one of the major processes for producing an amide compound, and it is known that in particular, acrylamide is produced from acrylonitrile as a raw material with ametallic copper catalyst, such as a Raney copper, and in recent years, with a hydration catalyst, such as a microorganism fungus body containing nitrile hydratase or a processed product of the microorganism fungus body.
In the foregoing process, a product, acrylamide, is generally supplied in the form of an aqueous solution or crystals, and upon using the same, it is generally used after diluting or dissolving with an aqueous solvent. Therefore, particularly in recent years, it is almost supplied in the form of an aqueous solution.
Upon supplying an acrylamide aqueous solution, those having a high concentration is demanded as a product form from the standpoint of the cost for transportation, storage and the like, but it is necessary that deposition of crystals is prevented during transportation, storage and the like. Therefore, the concentration of acrylamide that is suitable for transportation, storage or the like near ordinary temperature is generally about from 40 to 50% by weight.
However, the concentration of acrylamide in the reaction process in the conventional industrial production technique is generally less than 40% by weight while depending on the production process and the species of the catalyst used. This is because, in the case where the concentration of acrylonitrile and/or acrylamide in the reaction process is increased, there are such tendencies that the catalyst activity is lost, the reaction becomes incomplete to leave acrylonitrile as a raw material, the amounts of by-products are increased, and the like phenomenon, and such a problem occurs as restriction due to removing capability of reaction heat, whereby it is generally difficult that a final product having a product concentration of acrylamide is directly obtained when the foregoing reaction is completed.
Therefore, in the current industrial production process of acrylamide, the concentration of acrylamide is restricted, or the conversion rate of acrylonitrile as a raw material is suppressed to a low level by a method of supplying acrylonitrile as a raw material in a multistage manner (JP-B-57-1234), a raw material diluting method by circulating part of the reaction solution (JP-B-58-35077), and the like, whereby the concentration of acrylamide in the reaction solution is kept to less than 40% by weight to suppress the inactivation of the catalyst and the increase of the amount of by-products. Therefore, it is general that condensation is carried out to increase the concentration of the resulting acrylamide aqueous solution and/or to remove the remaining acrylonitrile.
While the condensation of the acrylamide-containing solution is generally carried out under reduced pressure, however, there is a danger of polymerization during condensation because acrylamide is a polymerizable monomer having an extremely high reactivity. Accordingly, such measures are carried out as a method of stabilization by introducing oxygen upon condensation, a method of co-existing nitrogen monoxide, a method of co-existing a metallic ion, and the like, but it is difficult that the polymerization is completely prevented.
JP-A-11-89575 discloses a production process of acrylamide by utilizing a microorganism fungus body or a processed product of the fungus body, in which acrylonitrile as a raw material is added in such a manner that the concentration of acrylonitrile at the start of the reaction or during the reaction is more than the saturated concentration of acrylonitrile in an aqueous medium, whereby a high acrylamide concentration can be obtained by a small amount of the fungus body. Although an acrylamide aqueous solution having a concentration of 40% by weight or more can be obtained without condensation, there are some cases where problems occur depending on the relationship between the used amount of the catalyst for the reaction or the reaction temperature and the concentration of acrylonitrile at the start of the reaction or during the reaction. For example, in the case where the reaction is completed in a short period of time, the heat of reaction in the initial stage is large to require a relatively large heat exchanger with respect to the reactor, and in the case where the conversion rate of acrylonitrile is 99% or more, on the other hand, a long reaction time is required.
Under the foregoing circumstances, such an industrial production process of an amide compound is demanded that the conversion rate of a nitrile compound is high, the condensation process is unnecessary, and an amide compound can be effectively obtained in a high concentration.